High density polyethylene (HDPE) made using certain late transition metal containing catalysts has lower water vapor and/or oxygen transmission rates than similar HDPEs made using other polymerization catalysts, thereby making them superior in uses, such as packaging, where lower water vapor and/or oxygen permeation rates are advantageous.
High density polyethylene (HDPE) is an important commercial product, large quantities being produced worldwide. HDPE is typically recognized (and is defined for the purposes of the present invention) as a substantially linear, semi-crystalline, polymer of ethylene (preferably a homopolymer but also on occasion containing very minor amounts of other well-known comonomers), possessing a density of 0.94 g/mL or higher.
An important use of HDPE is in packaging, which may be divided into two general typesxe2x80x94rigid packaging such as bottles and tanks, and flexible packaging such as bags and pouches. The former may be formed by such methods as blow or injection molding, and the latter are usually formed from films having one or more layers, at least one of which is HDPE.
HDPE is a favored packaging material for many products because of low cost, relatively easy formability and good toughness, and for some products having low permeation rates for certain materials either deleterious to these products, or to keep the package""s contents from diffusing from the package and being lost, such as water and/or oxygen. Among the types of products where these low permeation rates are important are foods, both dry and liquid materials, and lubricating oils. For example for dry foods low water vapor transmission rates are important to keep the foods crisp, while low oxygen transmission rates are important for any foods that may oxidize, forming off colors and/or tastes or smells in the food. The lower the transmission rates of the packaging, the better the food will taste and/or look, and/or the longer the food may be stored before being used, and/or the thickness of the packaging may be reduced without deleteriously affecting absolute rates of transmission, all of course important advantages. In some instances, such as bottles for toiletries such as perfume or cologne, it may be desirable to keep water in and/or oxygen out. Other combinations will be obvious to the artisan.
U.S. Pat. No. 5,955,555, WO99/12981, WO99/46302, WO99/46303, WO99/46304, WO99/46308, WO99/62963 (corresponding to U.S. patent application Ser. No. 09/317,104, filed 21 May 1999), WO00/15646, WO00/24788, WO00/32641, G. J. P. Britovesk, et al., J. Chem. Soc., Chem. Commun., p. 849-850 (1998), and B. L. Small, et al., Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) vol. 39, p. 213 (1998) (all incorporated by reference herein for all purposes as if fully set forth), all report the polymerization of ethylene using iron and cobalt complexes of certain tridentate ligands. No mention is made of the use of the resulting polymers for packaging where improved (lower) water vapor and/or oxygen permeation rates of HPDE are of interest.
Disclosed herein is a package comprising a high density polyethylene obtainable (and preferably obtained) by polmerizing ethylene in the presence of a polymerization catalyst component which comprises an iron or cobalt complex of a compound of the formula (I) 
wherein:
R1, R2, R3, R4and R5 are each independently selected from the group consisting of hydrogen, a hydrocarbyl, an inert functional group and a substituted hydrocarbyl; and
R6 and R7 are each independently selected from the group consisting of aryl and substituted aryl.
This invention also concerns a process for making a package, comprising the steps of:
(a) polymerizing ethylene in the presence of a polymerization catalyst component to form high density polyethylene, the polymerization catalyst component comprising an iron or cobalt complex of a compound of the formula 
wherein:
R1, R2, R3, R4 and R5 are each independently selected from the group consisting of hydrogen, hydrocarbyl, an inert functional group or substituted hydrocarbyl; and
R6 and R7 are aryl or substituted aryl; and
(b) forming said polyethylene into said package.
Preferably the package referred to above is a rigid storage tank or is otherwise based upon a multilayer sheet or film containing at least one layer of, or in which at least one of the layers comprises, the HDPE defined above.
This invention further concerns a process for lowering the water vapor and/or oxygen transmission rates of a package manufactured at least in part with a first HDPE, comprising the step of replacing, during the manufacture of said package, at least a portion of the first HDPE with a second HDPE obtainable (and preferably obtained) by polmerizing ethylene in the presence of a polymerization catalyst component which comprises an iron or cobalt complex of a compound of the formula (I) 
wherein:
R1, R2, R3, R4 and R5 are each independently selected from the group consisting of hydrogen, a hydrocarbyl, an inert functional group and a substituted hydrocarbyl; and
R6 and R7 are each independently selected from the group consisting of aryl and substituted aryl.
This invention still further concerns a process for lowering the water vapor and/or oxygen transmission rates of a package manufactured from one or more layers of a first HDPE, comprising the step of replacing, during the manufacture of said package, at least a portion of at least one of the layers of the first HDPE with a layer of a second HDPE obtainable (and preferably obtained) by polymerizing ethylene in the presence of a polymerization catalyst component which comprises an iron or cobalt complex of a compound of the formula (I) 
wherein:
R1, R2, R3, and R5 are each independently selected from the group consisting of hydrogen, a hydrocarbyl, an inert functional group and a substituted hydrocarbyl; and
R6and R7are each independently selected from the group consisting of aryl and substituted aryl.